This study examines ancient Roman ideas about humor’s boundaries in public culture. In particular, I analyze Book 6, Chapter 3 of the Institutio Oratoria, which covers Quintilian’s reflections on the subject. Following Cicero, Quintilian engages the tensions between humor and decorum in his political context, using urbanitas to refine the former and to loosen the latter’s strictures. In this process, the use of urbanitas implicitly points readers toward factors that can make humor rhetorical. Quintilian thus answers Cicero’s question about the degree to which humor should be used and furthers inquiry into how much rhetorical humor can or should be taught.